In recent times, there has been a heightened awareness on the part of the general public as to the environmental impact of certain types of aerosol propellants. In particular, aerosol propellants for paint, hairspray, insecticides, cleaners, and the like have been singled out as major contributors to depletion of the ozone layer which protects the earth from excessive ultraviolet radiation from the sun. This is due to the fact that for a number of years, aerosol containers contained propellants comprised of chlorofluorocarbons (CFCS) which, when liberated in the course of dispensing the product, reacted with the atmospheric ozone layer and caused it to become depleted. Chlorofluorocarbons typically consist of carbon, chlorine, fluorine, and hydrogen.
While most if not all use of chlorofluorocarbons has been eliminated in view of safer alternatives, many consumers continue to perceive aerosol containers in a negative light. Even though the environmental impact of aerosol containers has been reduced, widespread use of other chemical propellants may have other long-term consequences in the years to come. For example, volatile organic compounds (VOCS) such as butane, propane, and other hydrocarbons may contribute to pollution problems in the lower atmosphere.
These consumer perceptions have led to a resurgence in liquid dispensing containers which use no propellants at all. In particular, there has been a proliferation of pump-type spray devices which dispense a preset amount of liquid product with each stroke of a piston-type liquid pump. While improvements in dispensing valve and spray head technology have improved the quality of the resulting spray pattern produced by these devices, the consumer is still required to manually pump the piston numerous times to dispense the typical quantity of product required. The consumer thus receives a number of short spray bursts of product rather than a continuous, consistent spray as from an aerosol-type container. Many consumers find this dispensing mechanism too time and effort intensive, and find the spray burst method of operation unsatisfactory. Additionally, such pump spray mechanisms often produce different spray characteristics from an aerosol dispenser. Moreover, in order to achieve an acceptable pattern of spray, these devices often produce a very "wet" spray with too much liquid product dispensed per unit area for many applications.
An approach which has proven satisfactory in terms of consumer perceptions is the use of compressed air as a propellant. The liberation of compressed air has no negative environmental consequences beyond those of the liquid product itself, and such dispensing containers behave much like those aerosol containers which use chemical propellants in terms of spray quantity and quality.
One way to utilize compressed air is to prepressurize sealed containers at the factory with air, much like containers utilizing chemical propellants. The difference is, however, that with chemical propellants such as CFCs or VOCs, the propellants are actually in a liquified state in the container and boil as required to maintain a relatively constant vapor pressure in the container as the headspace increases during the course of product dispensing. In this fashion, a constant pressure is available throughout the course of dispensing the contents of the container to maintain uniform spray quality. With compressed air in a gaseous state, the pressure in the container decreases as the headspace increases in the course of product dispensing, leading to progressively poorer spray quality. With a conventional sealed container, the only ways to combat this tendency are either to use greater than normal volumes of compressed air or comparable volumes at higher pressures to dispense a comparable quantity of liquid product to containers utilizing chemical propellants. This means either larger containers for the same product quantity, or strengthened containers for higher pressures which are more costly. Even so, unlike chemical propellants which maintain a relatively constant pressure within the container during the course of dispensing its contents, with prepressurized containers utilizing compressed air the spray pattern will change as the air pressure within the container drops in use. Although the pattern may remain acceptable throughout much of the range of use, consumers will notice the inevitable difference in spray characteristics when the pressure varies to such a large extent, say from a typical 150 psi (1034 kPa) down to 30 psi (207 kPa) or less.
A solution which is currently being marketed is to design a container which the consumer pressurizes with atmospheric air periodically during the course of dispensing the contents of the container. This offers numerous advantages, including the possibility of making the containers refillable by the consumer to reduce costs and household waste, the non-chemical nature of the propellant, and the aerosol-quality spray characteristics. By allowing the air in the container to be replenished and additional air to be added to account for the increasing headspace as product is dispensed, a much more uniform level of pressure is available for dispensing without the need for a larger container or a special strengthened container. Such containers have an air pump apparatus, usually in conjunction with the dispensing valve assembly, for operation by the consumer to pressurize the container.
One such dispensing container for hairspray which is currently marketed in the United States comprises a plastic container with a removable valve/pump assembly such that the container is easily refilled by the consumer. U.S. Pat. No. 4,077,442, issued Mar. 7, 1978 to Olofsson, exemplifies this arrangement, and is hereby incorporated herein by reference. A removable pump piston attached to an upper cap surrounds the dispensing valve assembly and slides within an annular pumping chamber. This pump piston design utilizes a lip-type lower seal which contacts the outer wall of the chamber to form an air-tight seal, and an inlet valve immediately adjacent to the seal in the form of a slit in the piston wall. This pump piston also utilizes a small bleed hole in the piston wall to permit residual compressed air within the piston (from the final downward stroke) to bleed out such that the container can be stored with the pump piston installed in the lowered position.
The consumer reciprocates the pump piston to compress air within the confines of the piston/chamber combination and force it into the container through a one-way valve. Approximately 10-15 pump strokes are sufficient to initially pressurize the container (more precisely, to pressurize the headspace above the liquid in the container), and continuous dispensing is possible until the pressure in the container is reduced to the point where the spray pattern is no longer satisfactory. The consumer then re-pressurizes the container as needed throughout the course of dispensing the contents of the container. When the contents of the container are exhausted, the consumer can remove the piston, pumping chamber, and dispensing valve assembly, and pour an appropriate amount of liquid product into the container to refill and reuse the existing container. Upon reassembly, the consumer can then re-pressurize the container and again dispense the desired product.
Unfortunately, as the air pressure in the container decreases during use to a point below which spray effectiveness is greatly reduced, liquid product tends to dribble down from the spray outlet into the annular pumping chamber. When the pump piston is then inserted into the chamber and pumping is attempted, the inlet valve slit at the lower end of the piston becomes contaminated with the product. With some products this does not present any particular difficulty. With other products (such as hairspray) which become sticky when dry, however, exposure to air causes the liquid product to dry in and around the valve slit. The congealed product either effectively glues the edges of the valve slit together or prevents air-tight sealing of the opening, thus leading to degradation of sealing performance of the valve slit. As the performance deteriorates to the point of a complete inability to admit air into the piston or to effectuate air-tight sealing, the consumer finds himself or herself unable to pump sufficient air into the container for proper functioning.
The present invention is directed to improving the inlet valve design to protect it from exposure to contamination by liquid product, and thus improve reliability in the course of consumer usage. Specific attributes and advantages of this invention will be apparent with reference to the accompanying Specification and Drawing Figures.